EP 1 945 917 A1 discloses a control valve for a camshaft adjuster with a control sleeve arranged inside a valve housing and a hollow cylindrical control piston guided displaceably therein. Hydraulic medium can reach a control groove, formed on the control piston, via a hydraulic medium path from a camshaft-side supply, via an axial channel formed between the control sleeve and the inner casing surface of the valve housing, and via an opening in the control sleeve. From the control groove, the hydraulic medium can reach a supply port A and/or B depending on the switch position. The supply ports A, B may alternatively also be brought into connection with an outlet port T. The outflowing pressure medium is conducted to the cylinder head or the timing case via the outlet port of the control valve.